Turkey's military said it had had no contact with the eight soldiers after Sunday's clash and said 34 guerrillas had been killed so far in a counteroffensive. A pro-Kurdish news agency said the eight were captured — a claim that would make it the largest seizure since 1995, when guerrillas grabbed eight soldiers and took them to northern Iraq.

The ambush on Sunday outraged an already frustrated public. Demonstrations erupted across the country and opposition leaders called for an immediate strike against rebel bases in Iraq, despite appeals for restraint from Iraq, the U.S. and European leaders.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.

SIRNAK, Turkey (AP) — Dozens of Turkish military vehicles loaded with soldiers and heavy weapons rumbled toward the Iraq border on Monday after an ambush by rebel Kurds that left eight soldiers missing and killed 12. Turkey's foreign minister said his country will pursue diplomacy before it sends troops across the rugged frontier.

The military said it had had no contact with the eight soldiers after Sunday's clash and said 34 guerrillas had been killed so far in a counteroffensive. A pro-Kurdish news agency said the eight were captured — a claim that would make it the largest seizure since 1995, when guerrillas grabbed eight soldiers and took them to northern Iraq.

The ambush on Sunday outraged an already frustrated public. Demonstrations erupted across the country and opposition leaders called for an immediate strike against rebel bases in Iraq, despite appeals for restraint from Iraq, the U.S. and European leaders.

In Washington, the State Department said the United States has opened a diplomatic "full court press" to urge Turkey not to invade northern Iraq.

"In our view, there are better ways to deal with this issue," spokesman Sean McCormack said, stressing that the United States regards the PKK as a terrorist organization.

Prime Minister Recep Tayyip Erdogan said he told Secretary of State Condoleezza Rice in a telephone conversation on Sunday night that Turkey expected "speedy steps from the U.S." in cracking down on Kurdish rebels and that Rice, who called the Turkish leader, asked "for a few days" from him.

McCormack did not dispute the account of the conversation but declined to comment on what Rice had meant by asking for "a few days."

Erdogan did not specify what he meant by "speedy steps," but he has often urged the United States and Iraq to crack down on the Kurdistan Workers' Party, or PKK. Turkish leaders say it is the responsibility of those countries to do whatever is necessary to destroy the guerrilla group's bases in northern Iraq.

"We will continue these diplomatic efforts with all good intentions to solve this problem caused by a terrorist organization," Foreign Minister Ali Babacan told reporters in Kuwait. "But in the end, if we do not reach any results, there are other means we might have to use."

Babacan has been touring Arab countries to explain his country's plans.

The Turkish military confirmed Monday that eight of its soldiers were missing after the ambush by Kurdish rebels that left 12 other soldiers dead and brought the northern Iraq border area to the brink of war.

"Despite all search efforts, no contact has been established with eight missing personnel since shortly after the armed attack on the military unit," the military said in a statement on its Web site.

The pro-Kurdish Firat news agency, based in Belgium, released the names of seven people it said were Turkish soldiers captured by separatist fighters in Sunday's ambush. It said an eighth soldier was also taken captive but did not release his name.

The last major kidnapping was in 1995, when Kurdish guerrillas grabbed eight soldiers and took them to bases in northern Iraq, where the group is still headquartered. The rebels released the soldiers two years later after human rights activists, lawmakers and family members visited the rebel hide-out.

An AP Television News cameraman saw a convoy of 50 military vehicles, loaded with soldiers and weapons, heading from the southeastern town of Sirnak toward Uludere, closer to the border with Iraq.

It was unclear whether the vehicles were being sent to reinforce troops engaged in fighting with rebels on Turkish soil or were preparing for possible cross-border action. Tens of thousands of Turkish troops are already deployed in the border area.

More than 2,000 protesters in Istanbul, mostly members of an opposition party, denounced the attack by the PKK and urged the government of Erdogan to resign, the private Dogan news agency reported.

In Ankara, hundreds convened at a main square shouting "Down with the PKK and USA!" Ambulances decorated with Turkish flags drove around main streets, their sirens wailing.

Some 13,000 schoolchildren in Bilecik in eastern Turkey held a minute of silence while people marched down a main street, waving the Turkish flag, the state-run Anatolia news agency reported.

In Bursa, in northwest Turkey, some protesters walked to a military conscription office and asked to enlist to fight rebels.

Turkey's military said Sunday it had launched an offensive backed by helicopter gunships in retaliation for the attack, shelling rebel positions along the rugged Turkish-Iraqi border.

The rebel attack occurred four days after Parliament authorized the government to deploy troops across the border in Iraq, amid growing anger in Turkey at perceived U.S. and Iraqi failure to live up to pledges to crack down on the PKK.

Sunday's attack raised the death toll of soldiers in PKK attacks in the past two weeks to around 30.

Rebels periodically cross the border to stage attacks in their war for autonomy for Turkey's predominantly Kurdish southeast. More than 30,000 people have died in the conflict that began in 1984.

Out of respect for the soldiers killed Sunday, a concert by American R&B singer Beyonce Knowles in Istanbul was canceled, a soccer club that was organizing the event said on its Web site Monday.

Beyonce was to give a concert in Istanbul on Wednesday, as part of her world tour. "It was not possible for (the concert) to be held in such an atmosphere," the Web site quoted Ali Koc, vice president of the soccer club Fenerbahce.